The ink jet recording system is a printing method in which droplets of an ink are allowed to fly and adhere to a recording medium such as paper to perform printing. With recent innovative improvements in inkjet recording technology, the ink jet recording method has also come to be used in the field of high-definition image recording (printing) which has hitherto been achieved in the fields of photography and offset printing. Accordingly, high-quality recording has been required not only to plain paper and paper exclusive for ink jet recording (matte series and glossy series) which are generally used, but also to a recording medium such as paper for printing.
As the ink used in ink jet recording, there has been generally known an ink composition containing a coloring material acting as a coloring agent, water, a water-soluble solvent, a surfactant and the like.
As the coloring material, there is used a dye or a pigment, and particularly, a dye is used in a color ink in many cases, because of its high color saturation, transparency and high solubility in water. However, the dye is generally insufficient in terms of light resistance and gas resistance, and also has a problem in water resistance, because it is soluble in water. Accordingly, recorded matter in which recording has been made with the ink using the dye has the disadvantage of being poor in keeping properties of recorded images. In contrast, the pigment is a coloring material excellent in such light resistance, gas resistance and water resistance, so that development of pigment inks in which this coloring material characteristic is put to good use has been advanced. For example, there have been proposed an aqueous pigment ink in which the pigment is dispersed with a surfactant or a polymeric dispersing agent, an aqueous pigment ink using a self-dispersing pigment in which a water-dispersible functional group has been imparted to a surface of the pigment, and an aqueous pigment ink using fine colored particles in which the pigment has been coated with a water-dispersible resin.
In such pigment inks, the pigment particles (including the fine colored particles containing the pigment) are stably dispersed in ink solutions. However, when a ink cartridge is allowed to stand for a long period of time, or when the ink is left as being stored in an ink storage chamber of a printer, the pigment particles are gradually sedimented in the inside of the ink storage unit to generate a gradient in pigment particle concentration in the ink solution. For that reason, the difference in density is generated between ink density printed with the ink in an upper portion of the ink storage unit and that printed with the ink in a lower portion thereof. Accordingly, particularly in a recording method using two or more kinds of different colors, there has been the problem that not only the difference in density in monochrome is generated, but also the hue in color mixing changes to lose the color balance of a printed image to be originally obtained, resulting in deteriorated image quality.
Then, in order to prevent such deterioration of color balance, there has been proposed a method of specifying the degrees of sedimentation of respective inks of an ink set used for forming a color image, such as a yellow ink, a magenta ink and a cyan ink (see patent document 1).
Further, there has been proposed a method of substantially matching the degrees of sedimentation of respective inks by adjusting the compression void volume of a porous carrier impregnated with each ink in an ink cartridge to the sedimentation velocity of each ink (see patent document 2).
Patent Document 1: JP-A-2000-355667
Patent Document 2: JP-A-2001-328282
However, the degrees of sedimentation shown in patent document 1 are specified by combining the inks each selected increasing or decreasing the degree of sedimentation thereof according to a definite rule. According to this method, however, there has been the problem of insufficient improvement of deterioration of the gloss balance or color balance in image quality (photograph quality) on glossy media.
Further, the method of matching the degrees of sedimentation of respective inks by adjusting the compression void volume of a porous carrier impregnated with each ink in an ink cartridge to the sedimentation velocity of each ink is a means effective only for the ink cartridge equipped with the porous carrier. Accordingly, there has been the problem of the lack of flexibility.